Hundreds of Volunteers Join Search for Missing UVa Student Hannah Graham

— -- Nearly a thousand volunteers spread out through Charlottesville, Va., today to help in the seach for Hannah Graham, one week after the missing University of Virginia student was last seen.

Police told ABC News today that a person of interest who was seen going into a bar with Graham the night she disappeared was identified as Jesse L. Matthew, 32.

Graham may have gotten into a car with Matthew, and police said Friday they want to ask him "what he knows about Hannah."

Charlottesville Police Chief Timothy Longo said police spoke to Matthew Friday morning when they executed a search warrant and seized his car, but did not feel that they had enough probable cause to arrest him, Longo said.

Members of Matthew's family declined to speak with ABC News.

Parents of Missing UVA Student Hannah Graham Urge 'Walk With a Buddy'

'Person of Interest' Sought in Disappearance of University of Virginia Student Hannah Graham

Missing University of Virginia Student Hannah Graham Seen on Video

"We know that he purchased alcohol (in the restaurant) and we know that Hannah Graham was with him. We also know that within 15 minutes he was gone from that bar and Hannah Graham was with him," Longo said.

"People saw Hannah and people saw him, and people saw them together. And it's entirely possible, we believe, that Hannah Graham may have gotten into his vehicle," the chief said.

Longo asked for anyone to call police if they saw Graham get into the man's 1998 burnt orange Chrysler coupe.

While the person is not in custody, "We know who he is and we are aware of where he is," Det. Sgt. Jim Mooney said.

"I'm not calling him a suspect," Longo said. "We're interested in him, interested in talking to him, interested in what he knows about Hannah."

The chief would not say whether he believed Graham was still alive.

"I will always be hopeful until we find Hannah," he said.

Longo said he spoke with Graham's parents shortly before the news conference. "They want their daughter back. They want to know what happened."

Longo held his news conference after executing three search warrants on the car, an apartment and phone. He said that today's searches "absolutely" marked a major break in the case.

The first warrant was a search and seizure warrant for a vehicle that was executed shortly after midnight. When police arrived at the apartment building and seized the car, a person connected to the car was in his apartment with two others. Police identified those individuals, but the officer did not feel he had the grounds to detain the individuals, Longo said.

After seizing the car and taking it to an undisclosed location for the full search, investigators developed probable cause and sought approvals for the two other warrants. Police arrived back at the apartment shortly after 10 a.m. and the three individuals were no longer inside, Longo said.

The search warrants were issued a day after police announced a $50,000 reward for information about Graham's disappearance. Police had also released four clips of surveillance footage from local businesses that showed Graham, 18, walking around in the early hours of Saturday morning. She was last heard from around 1:20 a.m. Saturday when she texted friends, allegedly saying that she was headed for a party but was unsure of where she was.

A person of interest described by police Thursday came from a man who was seen following Graham on surveillance footage. That man told police that he was concerned about Graham because she looked "physically distressed," but he left when he reportedly saw another man approach her and put his arm around her.

That second man has been described by police as a person of interest. He is not seen on any surveillance footage.

Police described the person of interest as a black male in his 20s or early 30s, about 5-foot-10 or 5-foot-11 with a shaved head and goatee. He weighed between 250 to 285 pounds, has a slight beer belly and was wearing black jeans and a white T-shirt.

The FBI joined the case in a guidance role earlier this week and investigators are calling for volunteers as they plan a massive search Saturday. The volunteers are being asked to only join the search if they can walk four to five miles in a wooded area.